This application claims priority from European Patent Application No. 04106904.8 filed Dec. 22, 2004, the entire disclosure of which is incorporated herein by reference.
The present invention concerns a vibrating device, which includes means protecting against mechanical shocks, for a portable object, such as a wristwatch. The vibrating device includes a moving mass formed in part by a magnetic structure connected to a fixed structure by means of a spring element and a coil connected to the fixed structure with no mechanical contact with the moving mass. The coil is electromagnetically coupled to the moving mass to enable it to oscillate in at least one oscillation direction when it is being powered by alternating electrical signals at a determined frequency.
The vibrating device for a portable object can be used for generating a silent alarm or for indicating a telephone call by vibration. In order to do this, the coil has to be electrically activated to activate the moving mass in order to create a low frequency vibration that can be felt by the person carrying the object. The vibration can be controlled as a function of specific programming of the portable object so as to warn the user of a specific event, for example an alarm time, a telephone call etc.
The vibrating device can be fitted to a portable object, such as a wristwatch, a mobile telephone, a conventional organiser, a pager device or another object of small size. Since the vibrating device includes a relatively large moving mass with respect to the total mass of the device, it must be protected from any mechanical shock. Consequently, the moving mass of the vibrating device has to be prevented from undergoing movements due to shocks, in relation to the fixed structure, of too large amplitude in any direction. With such mechanical shocks, the spring element, holding the moving mass in relation to the coil connected to the fixed structure, can be subject to buckling or significant fatigue capable of quickly damaging or breaking the vibrating device.
An example of a vibrating device of small size is disclosed in EP Patent No. 0 625 738. In this document, the vibrating device is formed of a cylindrical coil mounted on a body of a ferromagnetic structure, a moving mass which includes a permanent magnet polarised in a direction parallel to the axis of the coil, and resilient elements connecting the moving mass to the ferromagnetic structure. The ferromagnetic structure includes electromagnetic excitation portions directed perpendicularly in relation to the coil axis, the excitation portions being opposite polar parts of the moving mass. When the coil is being powered by alternating electrical signals, the mass with the permanent magnet describes a quasi-linear oscillating movement.
One drawback of such a device disclosed in EP Patent No. 0 625 738 is that it is sensitive to shocks, since the moving mass has to be large in order for the vibrating device fitted for example to a wristwatch to provide a vibration capable of being felt by the person wearing the watch. Consequently, the resilient elements are likely to undergo significant deformations or to break during large mechanical shocks.